As a three-dimensional paper making technology, pulp molding is to mold paper products of certain shapes with molds in a pulp molding machine with the raw material as pulp or plant fiber.
One traditional production process for manufacturing pulp molded products includes the steps of: diluting plant fiber into pulp and placing it into a forming mold with a filter screen to form a paper embryo with a moisture content of 68-75% by mass percent through vacuum adsorption; reducing the moisture content to 10-15% through drying processes as drying in the sun, air drying or stoving, and placing it into a heat setting mold of 160-180° C. for reshaping through pressurizing. In this process, the product is almost dried and shaped in the stage of drying and has a density of 0.35-0.40 g/cm3 with obvious overlapping curves on both surfaces after reshaping through pressurizing; therefore, the method is often used for producing the packing material having a requirement for buffering rather than appearance.
Another traditional production process for manufacturing pulp molded products includes the steps of: diluting plant fiber into pulp and placing it into a forming mold with a filter screen to form a paper embryo with a moisture content of 68-75% by mass percent through vacuum adsorption; transferring the wet paper embryo into a heat setting mold with metal mesh screen for direct pressurizing, drying and molding. With a density of 0.6-0.65 g/cm3, the product of the method has one surface smooth and the other surface with obvious overlapping curves; the molded pulp packaging products and pulp molded cup lids on current market are produced by this process. Without effective press polishing, tiny plant fibers on the surface with overlapping curves are easy to be dissolved out; moreover, as molded in the mold with steel mesh screen, the deciduous tiny steel wires are easy to be pressed into the product, thus scraping the product and increasing the difficulty of production inspection.
The pulp molded cup lids in prior art are also produced through the processes as pulp diluting, vacuum adsorption molding, pressurizing, drying and molding under high temperature, edge trimming, suction port stamping, sealing edge stamping or annular trench rolling, etc., having one surface smooth and the other surface with obvious overlapping curves with a density of 0.6-0.65 g/cm3 as well. However, for aesthetic reason, the surface without overlapping curves is normally designed as the external surface of the cup lid and the other surface with overlapping curves as the internal surface; therefore, the dissolved plant fibers along with undetected steel wires may fall into the drinks, which is unacceptable for customers; in case the surface with overlapping curves is designed as the external surface of the cup lid, it will also be unacceptable for customers to swallow tiny plant fibers when their lips contact the surface with overlapping curves while drinking besides the unpleasant appearance of the product and non-moldability of literals and patterns.
Meanwhile, the density of the pulp molded cup lid in prior art is 0.6-0.65 g/cm3 for its forming with mesh screen, therefore, the using effect may be affected because the cup lid is likely damped and softened when contacting the hot drinks. Especially because of insufficient density of the sealing edge and no buckles, the cup lid and the cup rim cannot be connected and clasped and thus fail to achieve favorable sealing ability; when holding hot or cold drinks, the cup is easy to depart from the lid without buckles due to limited opening frequency and exogenic action and then scalds the user; the lid without buckles can no longer fit the cup rim tightly as the limited frequency is exceeded; the existing cup lid without stiffening ribs at the suction port side has low strength at the suction port, therefore, the suction port is likely to be softened and deformed when immersed by liquid especially the hot drinks and under the exogenic action applied by the labial part of the user.